Green roofs are becoming a growing staple in New York City architecture. These green spaces help to reduce the “urban island heat effect” by covering buildings in grass and plants that will take in carbon dioxide, convert it into oxygen and help to cool temperatures in some of the hottest months of the year. Columbia University has embraced this method of supporting the environmental health of NYC, and now boast seven green roofs totaling 18,180 square-feet in and around the college’s Morningside Heights campus. The roofs—which were installed between 2007 and 2008 using the Xero Flor Green Roof System—prevent as much as 420,000 gallons of stormwater runoff annually. This helps to alleviate pressure on New York City’s sewer system, which tends to flood and discharge toxic waste into the city’s waterways.

“Green roofs will help sustain not only the buildings where our students, faculty and staff work, but also the community in which we live,” said Joe Lenuso, Executive Vice President for Columbia University Facilities, on the college’s website. “The benefits that green roofs deliver to the environment – including cleaner air quality and energy conservation – relate to us all.”

Columbia’s green roofs are placed on residential buildings as well as student dormitories, and range from 650-square-feet to as much as 5,400-square-feet. The university is considering adding additional green roofs to the campus, including systems at grade level. Maintenance teams weed twice a year and apply organic and controlled-release fertilizer annually—a process which requires only a 30 to 60 minute time commitment per roof. Currently, the university is seeking sustainable irrigation system solutions for the roofs which may require additional watering in hotter months but may be cumbersome to reach with a traditional water hose or sprinkler system.

The green roofs were installed using Xero Flor pre-vegetated mats that roll out like sod and provide a lightweight system effective for some of Columbia’s older buildings structurally limited in maintaining heavy roof loads. The mats feature Sedum and moss vegetation grown in an engineered flexible textile carrier that can be rolled up, transported by a truck to the project site and rolled out onto the rooftop. A 2011 study by the university revealed that a green roof measuring about 10,750-square-feet could save $225 in annual cooling costs and between $330 to $350 annually in heating costs in New York.